Gas turbine engines generally comprise a compressor for compressing air flowing through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high energy gas stream, and a turbine which includes a rotor for driving the compressor. In addition, many gas turbine engines are of the turbofan type in which a fan located forward of the compressor is driven by a second turbine rotor. The fan produces a flow stream which bypasses the compressor, combustor, and turbine to provide propulsion.
One method of increasing the thrust output of the engine is to provide an augmentation system. Such a system injects additional fuel downstream of the second turbine which is ignited to provide an additional high energy gas stream. Prior to such ignition, the gas stream through the turbine is typically mixed with the fan airflow to provide increased oxygen for combustion.
In order to obtain proper mixing, the augmentation system includes a mixer with a generally cylindrical liner at its forwardmost end relative to the engine. This liner will generally line up with the cylindrical rear turbine frame. The gap between these two cylindrical members, liner and turbine frame, must be sealed in order to prevent premature mixing of turbine gas and fan air. Even in engines without an augmentor, it may be desirable to have a mixer which requires similar sealing.
The assembly of either augmentation system or mixer with the engine is complicated by the fact that each is normally located within the engine exhaust duct. This presents the problem of providing a seal for the gap between the two cylindrical members which is both reliable and easily installed.
Prior attempts to solve this problem have met with varying degrees of success. For example, "fishmouth" seals have been used in the past. Such seals include an axially extending recess on one member and an axially extending tongue on the other member which mate when the mixer and turbine frame are brought together. Fishmouth seals tend to be loose fitting so that some air/gas leakage occurs through the gap between the two members.
Seals employing piston rings have also been used in the past. These seals have a flexible ring which is retained by a radially directed recess on one member while maintaining contact with the second member. Seals with piston rings are effective, however, they are difficult to install and have also proven to be heavy and expensive to manufacture.